Microfiche Appendix Included (44 frames, 1 page).
1. Field of the Invention
The invention relates to a computer generated video imaging system, and more particularly to a digital map system for providing a real time moving display on a cathode ray tube.
2. Description of the Prior Art
Map displays are of primary importance to aircraft pilots in view of the hazards of low altitude flight over unfamiliar terrain where the terrain may be obscured by cloud cover or darkness. While paper maps can provide topographical features of the terrain, it poses a large burden on the pilot to try to calibrate the aircraft's position from a paper map on the pilot's knee. A digital map system electronically generates a map similar to the format of a paper map. It is desirable that such a display automatically calibrate the aircraft's position, show terrain elevation, and cultural and linear features such as roads, railroads, and rivers. One such system is described by Seitz, et al., in U.S. Pat. No. 4,484,192. A moving map display has a mass memory for storing a complete map of the terrain to be traversed by a vehicle A scan memory stores a portion of the complete map corresponding to the area immediately surrounding the vehicle. The portion of the map stored in the scan memory is updated by a computer and periodically refreshed for display on a cathode ray tube In this system, as the aircraft traverses the terrain, data in the scan memory is sequentially replaced on a column by column basis using a wrap-around scan technique.
Another system is described by Saito in U.S. Pat. No. 4,490,717. A plurality of drive route charts are stored in cassette tape memory and sequentially switched for display on a CRT as a vehicle travels a predetermined distance. The drive route charts are stored in memory as image information together with distance information. Distance stored in memory is updated by the actual travel distances of the car as predetermined check points are passed.
The present invention overcomes the disadvantages of the wrap-around storage system and the check point navigational system, both of which are slow in accessing data and updating memory, therefore rendering real time displays difficult The present invention provides an improved virtual memory storage and access technique for providing a real time display which permits overlaying data such as character symbology, contour lines, and dynamic sun angle shading in addition to the terrain data and for decluttering by selecting or deselecting individual features from the map for display.